The present invention relates to a positioning device, an electronic instrument, and a storage medium storing a program.
A global positioning system (GPS) is widely known as a satellite positioning system, and is utilized for a car navigation system and the like. The GPS allows the present position to be located by acquiring/tracking a GPS satellite signal from signals received from a plurality of GPS satellites, and performing positioning calculations based on a navigation message acquired from the GPS satellite signal and the like.
The GPS satellite signal is a spread-spectrum-modulated signal called a coarse and acquisition (C/A) code. A method has been widely used which improves the signal reception sensitivity by correlating a pseudo spread code (code replica) generated by a receiver and the received signal over a long period of time when acquiring the GPS satellite signal.
However, since the polarity of the received signal is reversed every 20 milliseconds (ms) according to the navigation message, when the signal used for the correlation calculation is acquired across the polarity inversion portion, the signal component is necessarily cancelled (hereinafier called “cancellation portion”). This hinders an appropriate correlation process, whereby the signal reception sensitivity (hereinafter simply called “sensitivity”) decreases.
JP-A-2005-321298 discloses technology which sequentially acquires signals while changing the signal acquisition timing from the signal reception start timing by a predetermined unit time, and selects the signal with the smallest cancellation portion.
However, since the technology disclosed in JP-A-2005-321298 uses a fixed unit time, the selected signal is cancelled to a large extent when the unit time is increased. For example, since a cancellation portion of up to 2.5 milliseconds occurs when the unit time is set at five milliseconds, the sensitivity cannot be increased.
On the other hand, the cancellation portion of the signal decreases by reducing the unit time. However, since the number of signals which must be calculated increases, the processing time increases to a large extent.